Wave varying and transmitting



June 5, 1928.

- R. A. HEISING WAVE VARYING AND TRANSMITTING Filed Aug. 15, 1923 4Sheets-Sheet Ra /m 0/7 d/I. fie/sing jiih 1928. 1,672,215

' R. A. HEISING WAVE VARYING AND TRANSMITTING Filed Aug. 15, 1925 4Sheets-Sheet 2 Wren/0r: Raymond A. Heis/ng by All June 5, 1928.1,672,215

R. A. HEISING WAVE VARYING AND TRANSMITTING Filed Aug. 15, 1925 4Sheets-Sheet 3 lhvenfor:

' Raymond AHe/s/ng y My June 5, 1928.

R. A. HEISING WAVE VARYING AND TRANSMITTING 0 m m 6 mH 0A w mm W oPatented June 5, 1928.

- UNITED STATES A 1,672,215 PATENT OFFICE.

RAYMOND A. HEISING, OI MILLBURN, NEW JERSEY, ASSIGNOR TO WESTERNELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEWYORK.

wave vemrme AND 'rlmnsmrr'rmo.

Application iiied August 15, 1923, Serial No. 857,488.

This invention relates to systems for and methods of producingelectrical waves and modifying them in accordance with signals or othereffects to be transmitted.

'Among the objects of the invention are to provide more efiicient modesof utilizing electrical energy in the production and modulation ofcarrier waves; to improve the power efliciency of electron dischargeamplifying systems; to modulate electrical waves with increasedeffectiveness and decreased distortion; to improve the modulatingefficiency of electron discharge device systems; to in crease theeffectiveness of modulation by the utilization of special waves of otherthan the waveform of speech currents; to carry each of the foregoingobjects into effect in combination with methods for wholly or partlysuppressing the unmodulated component of carrier frequency; and to carryeach of the foregoing objects into effect in connection with the methodof suppressing one side band of signal modulated waves.

In one embodiment involving certain features of the invention, speechfrequency and intermediate super-audio frequency waves of the same orderof amplitude are impressed together in the grid circuit of a vacuumtube. A resistance of suitable magnitude is connected across the gridand filament of this tube in such a'manner that impressed potentials ofconsiderably less than the peak value of the impresed waves cause thegrid to become positive to an extent limited by the relatively lowimpressed voltages and correspondingly limit the anode-cathode spacecurrent. The result is the production in the output circuit of a flattopped wave. A similar process can be repeated in several stages toincrease the flatness of the wave top and the steepness of its sides,thereby approximating a square topped wave, the production of which isfacilitated by using resistance couplings between the various tubestages and avoiding the use of inductance. Such a tube, or tandemarrangement of tubes, with appropriate input and output connections is,in this specification, hereinafter styled a wave former. The resultantelectromotive force produced by the wave former? is a succession ofsquare topped impulses which occur in regular sequence and atapproximately equal intervals but are of varying length-the variationbeing in accordance with the amplitude of the speech wave at successiveinstants of time. These uare topped impulses are impressed upon a argeinductance across which is connected a rec tifier and a condenser. Theaction of this rectifier-inductance combination is to produce asuccession of discharges into the condenserthe charge of the successivedischarges being proportional to the length of the corresponding flattopped impulses. A filter connects the condenser to an'oscillationgenerator which produces oscillations to be modulated.v The transmissionband of this filter is such as to pass freely all frequencies belowabout the mean of the intermediate frequency and the highest speechfrequency. If the intermediate frequency is 20,000 cycles, then thefilter may conveniently pass all frequencies below 12,000 0 cles andsuppress all higher frequencies. hus there is transferred to andimpressed upon the high frequency oscillator a modulating current oflarge energy which has been pro duced from a relatively feeble voicecurrent in a manner involving eflicient energy utili zation. Theintermediate frequency employed may range, in telephone systems, rom arelatively low to a relatively high value as, for example, 5,000 to200,000 cycles per second and the high frequency may extend over asimilarly wide range for ex ample, from 100,000 to several millioncycles per second. Illustrative values are: intermediate frequency,20,000 cycles; transmission limit of cut-off filter, 12,000 cycles; highfrequency, 100,000 cycles per second.

Certain modified forms of the invention are described hereinafter, theparticular na ture of each modification bein briefly set forth inconnection with the fol owing brief description of the several figuresof the drawing to which reference is made for a more completeexplanation of the nature, objects and advantages of the invention andthe methods of carrying it into effect.

Fig. l is a circuit diagram of the essential elements of an embodimentof the invention in which a wave former is used to transform modulatedoscillations into flat topped impulses whose length is modulated andwhich are then impressed upon a high frequency generator to cause it toproduce modarrangement in whic a separately excited I high frequencyamplifier is substituted for the oscillator or, in other words, for thatortion, of Fig. 1 to the right of the line W; Figs. 2, 3, 4, 5, 6, 7, 8,9 and 10 are current and voltage diagrams for explaining the operationof the system of Figs. 1 and 1*.

Fig. 11 is a circuit diagram of the essential elements of a form of theinvention in which a key-interrupted wave is impressed upon an impulseamplifier which is irectly coupled to an antenna; Fi 11 is a modifiedform of Fig. 11 in whic an arrangement for roducing a single side bandof a speech mo ulated wave is substituted for the devices of Fig. 11which produce the key-interrupted wave; Fig. 11 is a modified form inwhich an entire modulated wave takes the place of the key-interruptedwave; and Fig. 11 is a modified form in which the power tube amplifierof the system of Fig. 11 is supplied with a speech modulated currentsupply.

Fig. 12 is a circuit diagram of the essential elements of a form of theinvention in which a modulated wave from which the unmodulated componentof carrier frequency is suppressed, is radiated; and Figs. 13 and 14 arediagrams for explaining the operation of the system of Fig. 12.

Fig. 15 is a circuit diagram of another arrangement for transmittingwaves from which the unmodulated carrier component frequency has beensuppressed; and Fig. 16 is a diagram forexplaining the operation of thearrangement of Fig. 15.

In Fig. 1, the microphone circuit 1 indicates any suitable source ofspeech or signaling waves, such as a telephone line. An oscillationgenerator 2 supplies carrier waves of a suitable frequency, for example,20,000 cycles. The speech and carrier waves are impressed upon tworesistances 3 and 4 arranged in series. The resistance 3 together withthe olarizing battery 5 is included in the grid-filament circuit of anelectron discharge repeater 6. In order to simplify the followingexplanation, let it be assumed that the generator 2 is operating butthat no waves are being produced in the microphone circuit 1. Thebattery 5 and the resistances 3 and 4 are so proportioned with respectto each other and with respect to the amplitude of Waves produced by thedevice 2 that positive half cycles of the 20,000 cycle waves impressedby device 2 upon the grid-filament circuit of the device 6 render thegrid so positive that the space current consists of flat toppedimpulses. Furthermore, the bat-- tery 5 is of such electromotive forceas to produce a normal condition of zero or very small space currentfrom the plateto the cathode of the tube 6. The operating results may beexplained by reference to Fig. 2. In Fig. 2, the line ()A represents thezero axis; the line V represents the normal negative potential of thegrid; the sinusoidal curve W represents the impressed wave; and theflat-topped curve I represents the resultant space or plate-filamentcurrent. Current I thus approximates a series of flattopped impulses. Bya succession of steps each comprising an amplification of the impressedflat-topped Wave and the cutting off of such am lified wave theamplitude and energy of t ese impulses may be increased and their waveform may be made to approximate a fiat-topped and perpendicularly sidedseries of impulses within a sutficient degree of approximation, therebyproducing the theoretically correct wave form indicated by L, in Fig. 4.

The condenser connected in series with resistance 7 in the outputcircuit of the tube 6, serves to prevent direct current from traversingthis path, but permits alternating current to flow through theresistance 7. An increase of current flowing in the platefilamentcircuit of the tube 6 produces such a change of current flowing throughthe resistance 7, which is included in the input circuit of the tube 8,as to make the grid more negative. Consequently, it may be advisable notto have a normally zero space current through the tube 8, but to have afinite value of space current which is reduced to zero. The degree ofpolarization of the grid of tube 8 is much less than the change ofpotential which is produced by the maximum increase of current throughthe plate filament circuit of tube 6. This condition is illustrated inFig. 3 where L, similarly as in Fig. 2, represents the resultant impulsecurrent flowing in the plate-filament circuit of tube 8, its maximumvalue (unlike the maximum value of the corresponding current in Fig. 2)being the space current normally flowing through the tube, and IVrepresents the summation of alternating components of the currentflowing through the plate-filament circuit of tube 6, which is oppositein phase to the potential wave impressed on the grid of tube 8. For thecase illustrated it is assumed that the biasing potential of the grid oftube 8 is normally so great that the positive half waves of potentialimpressed on it (corresponding to the negative half wave of current IV)are not effective for increasing the current flowing' in itsplatefilamcnt circuit. WVit-h other adjustments of the normal biasingpotential, this current could be made to increase from the normal valuebefore flattening, as well as to decrease to zero. As an alternativearrangement, it may be desirable to reverse the connections of the inputcircuit of the tube 8 to the resist ance 7, as shown in Fig. 1. which isan alternative arrangement for that portion of the circuit of Fig. 1comprised between the dotted lines PP and Q-Q and using a zero normalspace current. In Fig. 1, an increase of current through the resistance7 rent relations will be as indicated in Fig. 2

with the exception, of course, that the impressed wave W will beflat-top ed as in ig. 3 and the operations invo ving this tube will bethe same as those involving tube 6. .If additional tubes are used in theprocessof forming the wave their operations may partake of either of theabove described modes of operation, or of that described in the nextparagraph.

It should be understood that, also with the connections as shown in Fig.1, as distinguished from those shown in. Fig. 1 which have been treatedimmediately above, the tube 8 may have its grid polarized so thatnormally no space current will pass. In

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such a case,the variation of current to produce the impulses'resultsfrom the negative half waves of the-current W, that is, the

positive half waves of the potential impressed on the grid of tube 8.This operation is strictly analogous to that of the modificationillustrated by Fig. 1, differing only in that use-is made of differenthalf waves of the current W. Ingeneral the grid Voltage of tube 8 mayhave any value provided the operating condition is such that a change ofgrid voltage results in achange of space current flow.

Figs. 2, 3 and 4 may therefore be assumed to indicate the successivechanges which occur as the result of the operation of a glurality 'oftubes, such as 6 or 8, or a comination of them, it being assumed thatpoints lying in a vertical line one above the other in Figs. 2, 3 and 4indicate correspondin instants of time in the several figures and iteing understood that an indefinite number of such operations may beinvolved, the number depending on the degree of angu larity, and theamplitude, desired in the finally produced wave. The curve 1,, (Fig. 4)represents the ideal form of resultant electromotive force in theanode-cathode circuit of the last tube in such a series and the spacecurrent therethrough on the assumption that the external lmpedance werea uniform resistance. The tubes 6 and 8 and their associated elementsmay be considered to be a wave former, the object of which is to converthalf cycles of a sinusoidal imressed wave into corresponding flat-toppedimpulses. The operation of the wave former is improved by avoidinginductive reactance in the input and output circuit-s of the tubes.

The tube 9 may be viewed as an intermediate frequency power amplifierhaving normally zero space current. The fiat-topped impulses illustratedin Fig. '4 are impressed on its input circuit. The grid of'this poweramplifier is made positive at a (Fig. 4) and negative at b (Fig. 4). Theplate circuit of the tube 9 includes a battery 12 of high electromotiveforce and little reactance and a coil 13 of high inductance. Across thecoil 13 is connected a rectifier 14 towhich is connected a filterdesigned to pass all frequencies below 12,000 cycles per second and toexclude all materially higher frequencies. To the output side of thefilter 15 is connected a vacuum tube 16 which functions as a generatorof oscillations in the antenna circuit 17. The oscillation generator maybe of any known type which will produce oscillations modulated inaccordance with variations in the direct current supplied thereto. 1

In Fig. 5 is shown a series of curves for explaining the operation oftube 9 and the rectifier 14. When the grid of tube 9 becomes positive asat points a (Fig. 4) the impedance of the tube 9 becomes very small.Almost the entire voltage of the battery 12 is then impressed across theinductance 13 and the current through the inductance begins to rise asshown in the curve 0 (Fig. The current continues to rise through theinductance until the grid of the tube is again made negative, as atpoint I) (Fig. 4).

When this occurs, there is a large current the rectifier 14, thedescreasing current following the curve (5. The voltage across theinductance 13 follows the wave form of the curve 6 (Fig. 5). The'curve f(Fig. 5) represents the voltage across the condenser 18. When thecurrent through the coil 13 is increasing. the voltage across thecondenser 18 is slowly falling. \Vhen the coil 13 discharges through therectifier 14, an additional charge is forced into the condenser 18,thereby increasing the voltage there across. The curve 7 comprises afundametal frequency corresponding to the frequency of the intermediatecarrier frequency source 2 with various harmonic components. \Vhen thevoltage corresponding to the curve I recurs regularly the currentsupplied to the oscillation generator 16 will be substantially constantand the oscillations produced will be constant. As pointed outhereinafter, the filter 15 suppresses not only all frequencies in theneighborhood of the frequency of the source 2 but of higher frequencies.(The curves on the bottom axis of Fig. 5 do not apply to Fig. 1 but areused hereinafter in explaining Fig. 11.) The operation. as so fardescribed relates to the condition in which no waves are being producedin the microphone'circuit 1 and no modulation is being effected.

The operation of Fig. 1 as a modulating system when waves are beingproduced in the microphone circuit 1 will now be explainetl by referenceto Figs. 6, 7, 8, 9 and 10. In Fig. 6. OA represents the zero axis; thecurve S the signaling voltage introduced in the microphone circuit 1;and C the voltage of the intermediate carrier fre uency. As shown inFig. 6, the voltage 0 the intermediate carrier frequency is superposedupon the signaling current S so that the curve C in Fig. 6 may be takento represent the voltage impressed upon the input circuit of the vacuumtube 6. Curve D (Fig. 6) represents the maximum current flow in theoutput circuit of tube 6. Hence, as shown in Fig. 7, there will beproduced in the plate circuit a series of impulses of variable lengthresulting from the peaks of the input impulses of higher amplitude beingflattened or cut off. By repeating the wave forming process as often asnecessary, the series of impulses indicated in Fig. 7 will assume theform indicated in Fig. 8, wherein all the impulses are of substantiallyuniform amplitude but vary in length proportionally to the maximumamplitude of that particular portion of the curve C (Fig. 6) from whichthey were derived. The net result is to form a series of impulsesmodulated in length rather than amplitude. These impulses represent thevoltage applied to the grid circuit of the vacuum tube 9. The gridvoltage of this tube is normally adjusted to pass little or no spacecurrent. As shown in Fig. 5, when the impulses are assumed to be ofuniform length, current through the inductance 13 arises to the sameamplitude as a result of each impulse. When the impulses are modulatedin lengthor duration, as indicated in Fig. 8, the current through theinductance 13 will rise each time to a height approximately proportionalto the length of the corresponding impulse. This condition isillustrated in Fig. 9, wherein -are indicated a series of currentimpulses g, h, z" and is through the inductance 18 corresponding to aseries of impulses g, h, 2' and lo of-varying length impressed upon thegrid of the tube 9. The maximum values or amplitudes of the series ofimpulses g, h, 2' and k are proportional to the maximum values, oramplitudes, of the impressed signal waves. These values areindicated bythe series of ordinates g, h", z', and is", (Fig. 10). The energytransferred to the oscillator is proportional to the square of theseamplitudes since the energy transferred to the capacity from theinductance in each cycle is A; LI whereI is the maximum current in theinductance and L is the inductance. This is exactly what is desired,since the envelope of these amplitudes has the form of the impressedsignal wave. As the filter 15 is designed to pass current variations ofall frequencies below 12,000 cycles per second, the signaling frequencyvariations will be transferred through the ,the signaling currents inthe microphone circuit 1. These high frequency carrier currents may beof large power if the amplification occurring in the wave former 6, 8 issufficient to produce energy capable of modulating high poweroscillations. The necessary amplification of the speech currents can beeffected in a system of this type in such manner that the total energysupplied to the amplifier system is efficiently utilized due to the factthat the vacuum tubes are practically all the time working at zerocurrent and high impedance (resistance) or finite current and lowimpedance (resistance). For this condition, which is identified by theangular characteristic of the wave, the losses in the plate-filamentcircuit of the tubes is low and the efiiciency correspondingly high. Thepower for the higher frequency generator does not come direct from anordinary current supply source but is produced by rectification of thespecial form of fluctuating current wave supplied by the wave formerdevice. The modulation results entirely from the proper varying of thespecial wave.

In Fig. 1* is illustrated one of the possible forms of high efficiencyoscillation generators which may be substituted for "the oscillationgenerator 16. Fig. 1 therefore is a substitute for that portion of thecircuit of Fig. 1 which lies to the right of the broken line WW. In Fig.1 a triode oscillator or other source 20 furnishes sinusoidal carrierwaves of any desired frequency, for example. 100,000 cycles. These wavesare amplified by an amplifier A and supplied to a harmonic generator HG,a device well known in the art, which produces a series of multiplefrequencies including the triple frequency component i. e. 300,000cycles. The triple frequency component is selected by any suitable typeof selective circuit SC conveniently illustrated as a simple tunedcircuit. The selected triple frequency component is amplified to anydesired extent by a thermionic amplifier A The amplified triplefrequency component and wave energy from the source 20, furtheramplified if desired by amplifier A are both impressed upon a circuit21. A phase shifter PS, a device well known in the art, is adjusted tochange the phase of the triple frequency component, if any change isnecessary, so that it has the phase relation with respect to thefundamental necessary to produce a wave of peaked wave form. The wavesin the circuit 21 constitute the carrier wave which is to be modulatedin accort'lance with speech or other signals. The circuit 21 comprisesthe in ut circuit of a hi h efiiciency power ampli er or modulated highfrequency producer 22. Across the grid-filament circuit of the amplifier22 is connected a rectifier 23 in series with a variable resistance 24.The elements 23 and '24 are shunted with res ect to the grid-filamentpath of the tube 22 y a variable resistance 25 and a condenser 26. Agrid porlarizing battery 27 is adjusted to such a value that only asmall or negligible space current flows in the amplifier 22 when nowavesare being supplied from the source 20. Incoming high frequency wavesfrom the am lifier A, and the phase shifter PS have their energypartially fied and cause the grid potential of t e tube 22 to fall to astill more negative value. Only the peaks of the incoming .waves tend tocause space current to flow in the amplifier I 0 22. The space currentsupplied to the amplifier 22 is a speech modulated wave supplied fromthe output circuit of the filter 15. The

antenna circuit or radiating aerial 28 is referably sharply tuned to thefundamental requency of the source 20 i. e. 100,000 cycles per second.The waves of peaked waveform supplied to the input circuit of the poweramplifier 22 impulsively excite the antenna circuit 28 to producetherein high frequency oscillations. The impulsive excitation andconsequently the amplitude of the produced waves is varied in accordancewith the signaling waves in the circuit 1.

Fi 11 represents a modified form in whic the waves radiated by theantenna circuit are of the same frequency as those supplied b carriersource 2 which may have any suitable frequency as, for example 100,000.The waves from the source 2 are supplied through a'series of elements 3,4, 5, 6, 7, 8 and 9 which function as the correspondingly identifiedelements of Fig. 1 function when carrier waves only, without signalingwaves, are applied. Fig. 11 may be modified in accordance with Fig. 1*in the same way as Fig. 1 may be thus modified. A telegraph key forinterrupting the waves I in accordance with a code is a typical form ofsignaling device which may be used in this circuit. The waves suppliedto the device 30 from the tube ,9 and inductance 13 constitute a uniformseries of im ulses, such as e (Fig. 5). The operation 0 the device 30and its associated elements will now be described. v

The device 30 is a vaccum, tube repeater of the three-electrode typehaving associated elements so arranged as to increasethe operatingefiiciency. For more perfectly illustrating its operation, referencewill be made to Fig. 5, including the curves on the lowest axis of thefigure.

The curve a represents the current through the inductance 13 and thecurve e the voltage across this inductance. Y The curvef is repeatedupon the the condenser would fall recti-' bottom axis and represents thevoltage across the condenser 31 upon the hypothetical assumption thatthe condenser was shunted by a resistance of suitable finite value. Theactual voltage across the condenser 31 is represented by the irregularcurve consisting of the sections l, m, n, 0, and p. When the inductance13 discharges into the condenser 31, the condenser receives anadditional charge represented b the portion of the curve marked m. f thecondenser 31 were shunted by resistance 7 the voltage across off inaccordance with the curve f. However, at the time the condenser is chared up in accordance with the portion of t e curve m, it begins todischar e through the inductance 32. As the con enser 31 andtheinductance 32 form a resonant combination, the discharge of thecondenser will be carried so far as to char e the condenser partially inthe oppositeirection, thereby causing the potential across it to execute"a portion of a damped sinusoidal curve n. However, at about the timethe first cycle of the curve 1 has been com-- pleted and the curve n hasswung above the axis to touch the curve f, the condenser will suddenlyreceive another charge, thereby raising its potential in accordance withthe portion of the curve 0-. This cycle of operation will be repeatedover and over. Inasmuch as the curve Z, m, n, o and p is approximatelysinusoidal, the tuned antenna 33 will be caused'to execute sinusoidaloscillations. The energy transferred to the antenna from the circuit 31will be principally of the frequency of the fundamental wave.

As shown at the bottom of Fig. 5 the condenser 31 after being charged upbegins to oscillate in combination with the inductance 32 as a partof atuned circuit and the voltage across the condenser proceeds to executethe curve n. When the voltage across the condenser 31 reaches its lowestpoint, as indicated at the lower part of curve n, the condenser tends tosend current through the plate-filament path of the tube 30 and theinductance 13. This is prevented b having the coil 34 connected to andso in uctively related to the coil 32 that as soon as the con-v denser31 and coil 32 are positive on their lower terminal as compared to theupper terminal,-the coil 34 willhave an electromotive force induced initself, which makes the gridnegative with respect to the filament. Thiscauses the impedance of the tube 30 to rise to such a value that theenergy stored in the condenser 31 cannot be dissipated by sendin currentthrough any path except throug the coil 32. When the voltage on thecondenser has executed almost a complete cycle so as to reach the pointwhere the curve 12 touches the curve f, the lower side of the condenser31 is negative with respect' to the filament of 'tube 30 and theinductive connection between coils 32 and 34 causes the grid of the tube30 to become positive with respect to the filament. The resistance 35prevents the grid from becoming positive more than a few hundred voltswith respect to the filament, assuming that the maximum plate voltage isof the order of several thousand volts. The best condition is to havethe grid become positive by that amount which will cause theanode-cathode resistance of the tube 30 to be a minimum. The tube,therefore, will have low impedance during the time when current shouldpass through it, and will have practically infinite impedance at thetime when no current should pass through it. The succession ofdischarges by the inductance 13 into the condenser 31 causes the voltageacross the condenser to have the irregular shape indicated in Fig. 5,but this can be resolved by the principles of Fourier analysis into afundamental wave and numerous harmonics. The harmonics will belargelyeliminated by the tuning of the antenna circuit 33.

The operation of the system of Fig. 11 is such as to produce in theantenna 33 hi h power waves of the frequency produced y the low powersource 2. In Fig. 11 is shown a. key 36 for interrupting the waves inorder to signal. Tubes 9 and 30 operate in a highly efiicient mannerinasmuch as they have at all times either a large current flowingthrough a small tube resistance or practically zero current flow whenthe tube resistance is large.- Likewise the tube 6 is operated in asimilar highly eflicient manner, although the power saving in the caseof this tube is less than in the case of the tubes 9 and 30, whichhandle much larger energies. Since the tube 8 when operating asdescribed normally has finite space current, its efiiciency will besomewhat less. The power handled by the tube 8 is intermediate that ofthe tube 6 and the tube 9. However, by reversing the connections of thetube 8 in the manner indicated in Fig. 1*, or by adjusting the normalspace current to zero like tube 6, operation will be satisfactory,

and ,it may be made to function as efiiciently as the tubes 6 and 9.

Systems similar to Fig. 11 may operate to transmit speech or othermodulated waves as well as waves of uniform amplitude. Fig. 11 shows amodified arrangem :nt which may be substituted for that part of Fig. 11to the left of the line XX which is adapted for transmission of one ortwo side-bands of a modulated wave with the carrier suppressed. In theoperation of this modified form, the key 36 should be permanently closedor replaced by a permanent connection. The modified apparatus consistsof a well-known type of balanced modulator 37 consisting of theoppositely connected tubes 38 nd 39, to the input circuit of which isconnected a source 40 of high frequency waves and a source 41 of speechfrequency waves. The operation of such a balanced modulator arrangementis well known. (See pa er by Colpitts and Blackwell entitled, arrierCurrent Telephon and Telegra by in the Journal of A. I. E., Vol. 40,Kpril 1921.) A band-pass or other filter 42 preferably suppresses oneside-band of the modulated wave, although it is optional to have thefilter 42 transmit both side-bands thereof. The operation of Fig. 11modified in accordance with Fig. 11 will be obvious from the precedingvdescription.

Fig. 11 is a modification of that portion of Fig. 11 to the left of theline R-R, and

is adapted for the production and transmis-- sion of modulated wavesfrom which the unmodulated carrier component is not suppressed. Theelements 2, 3, 4, 5 and 6 function as described in connection with Fig.11. The microphone circuit 41 supplies modulating waves. The tubes 6 and8 constitute a wave-former and the inductance 13 an energy storingelement. The current impulses discharged into the condenser 31 from theinductance 13 will vary in amplitude in accordance with theinstantaneous amplitudes of the speech modulated waves introduced intothe system. Correspondingly modulated waves will be radiated from theantenna 33.

Fig. 11 shows a modification of that portion of Fig. 11 to the right ofthe line Y-Y. In. this arrangement continuous waves produced by thesource 2, after passing through the wave-former, actuate the tube 9,which is provided with a speech modulated current supply. The tube 9therefore acts as a circuit opener and closer for commutating energy atthe rate set by the high frequency wave which is established bythesource 2. The power supply for the tube 9 may consist of any suitablepower modulating system, such as a constant current or constantpotential system. The drawin illustrates a constant current system inwhich a plate current source 43 supplies current to the tubes 9 and 45in parallel through a circuit including highly inductive speechfrequency choke coil 44. Tube 45 ,is controlled by the microphonecircuit 46. Modulated high frequency impulses will be discharged throughthe tube 30 into condenser 31. The condenser 31 will oscillate inconnection with the coil 32 and set up oscillations in the antenna 33 asdescribed in connection with Fig. 11. The coil 34, the resistance 35 andthe rid of the tube 30 are used as in Fig. 11 an function in a similarmanner.

Fig. 12 illustrates an arrangement more desirable in some respects forthe transmission of carrier Waves from which the unmodulated componenthas been suppressed. The source 1 and the carrier wave generator one orthe other of the tubes.

2 are coupled to the input circuits of two oppositely relatedwave-forming systems. The tubes 6 and 6 constitute the first members ofthese systems. Between each pair of lines ZZ and ZZ may be connectedone, two, or more additional wave forming tubes of the type indicated inFig. 1 betweenthe lines ZZ. Each wave forming system supplies asquare-topped wave to the input circuit of tubes 9, 9 which feed intoenergy storing inductances 13 and 13. which in turn supply impulses ofcurrent through the tube 30 and 30. Each of the tubes 30 and 30 set uposcillations in their respective tuned output circuits 31, 32 and 31.,32',

thereby impressing the oscillations upon the antenna 33.

The operation of the system of Fig. 12 may be elucidated by reference toFigs. 13 and 14. In Fig. 13, E0 represents the negative grid voltageupon the respective wave forming tubes 6 and 6. This voltage is suchthat nospace current flows in either tube even with a fair highfrequency voltage, represented by curve HF, impressedupon the inputcircuit. The high frequency voltage is preferably so adjusted as to justcause the grid potentials of the tubes 6 and 6' to rise at the peaks topoints where space current will just about, but not quite, begin toflow. If now a signal wavc is introduced from the microphone circuit,these peaks will operate from the characteristic curves on The dottedlines 9 indicate the cut-off grid potential, at which further increaseof grid voltage causes little or no additional space current flow andthe solid lines 7 indicate the intermediate position to which the gridvoltage should rise during signaling. The operation is such as to causethe two separate parts of the carrier wave to go through separate waveformers. Thus, as indicated in Fig. 14, where S represents the signalingwave,

there will be a. positive series of impulses going through the waveformer connected to.

tube 6 and a negative series of impulses connected to the tube 6',which, however, as will be noted, is in opposed relation so that eachwave former will function in a similar manner, although out of phasewith each other with respect to the signaling wave.

The resultant wave produced in the antenna 33approximates a modulatedwave from which the unmodulated component of carrier frequency has beensuppressed. .The energy represented by the unmodulated component is notradiated. The wave formers 48 and 48' may consist of any desired numherof tubes arranged in tandem. or of a single tube if desired.

In Fig. 15 is shown an arrangement adapted for producing a modulatedwave of such high frequency that itcannot be transferred through thewave forming devices in an efiicient manner owing to the internalcapacfor example, 10,000 to 500,000 cycles. per' second. The arts ofFig. 15 which are identified by t e same reference characters as in Fig.12, function in a. similar manner. Filters 49 and 49 correspond tofilter 15 of Fig. 1 and are designed to pass'a range of frequencies upto and including the highest frequencies essential for the reproductionof the modulating waves introduced in the filter circuit. Rectifiers 57and 57 function in the same manner as similar device 14 of Fi 1. Thatis, in cooperation with the in uctances 13, tubes 9 and 9' andcondensers 58 and 58' (which function in the same manner as condenser 18of Fig. 1) they convert the series'of impulses, corresponding to thoseillustrated in Fig. 14 after having been formed into equal amplituderectangular impulses having different widths, into a wave having theform of the original signal wave. Each set of elements thereforereproduce, one half the signaling wave so that when such half waves areimpre:sed'

uponthe amplifiers 50 and 50. the resultant wave in the antenna circuit33 will be a pure modulated wave. The amplifiers 50 and 50' as I aresupplied at their .input circuits with vthe tubes 50 nd 50 is thusderived from the'waves supplied by the sources 1 and 2, amplified by thetubes 6 and 6', and transformed by the wave formers 48 and 48and thetubes 9, 9, 30, 30 and their associated elements. The high frequencysource 51 acts as a commutatmg arrangement tovary the impedance of thetubes 50, 50. High frequency choke coils 55, 55 prevent the high carrierfrequency current from flowing into the filters 49, 49'. The stoppingconimpedance to speech frequency waves. In Fig. 16 thecui ves s and trepresent the current supply to the amplifiers 50 and 50 from thefilters 49, 49'. The curve a (whole line) indicates increasing currentsu ply to the amplifier 50 as it recedes from't e axis and the curve It(dotted line) indicates increasing current to the amplifier 50 as itrecedes from the axis.

From a consideration of the various ardensers 56 and 56' are ofrelatively high 12 rangements herein specificall described, it will beapparent to those ski led in .the art that a large number ofcombinations of h gh efliciency generating devices, wave formingdevices, modulating devices and amplifying devices, all of which operatein accordance with the same general principles, may be made. Forexample, the elements 20, A, A HG, SC, A PS and A of Fig. 1 may besubstituted for the elements 51, '52 of Fig. 15.

Having described the various systems involving the invention, thevarious parts, circuits, combinations and methods which are believed tobe novel are set forth in the appended claims.

I claim:

1. The method of modulation which comprises producing a series ofimpulses of duration varying in accordance with a'signal and convertingthese into a corresponding series of impulses of amplitude varying inaccord ance with a signal.

2. The method of modulation which comprises producing voltageimpulsesofsubstantially flat topped wave form, and introducing thereinto amodulation variation which consists principally in changing the lengthor time duration of the successive impulses.

3. The method which comprises producing impulses which succeed eachother at a rate above the usual frequency of audible speech waves andmodulating said impulses in accordance with a speech wave byicausingsuccessive impulses thereof to vary in energy content principally bychanging their duration in accordance with successively differentinstantaneous values of the amplitude or current energy of the speechwave.

4. A system comprising a wave generator and means for producing waves inwhich signals to be transmitted are represented by the duration andfrequency of current impulses rather than by their amplitude.

5. The method which comprises producing a series of impulses of lengthor duration varied in accordance with a sound wave and converting theimpulses into corresponding impulses of substantially uniform durationand of amplitude varied in accordance with the sound wave.

6. A system comprising a signaling wave source, means for producingimpulses whose time duration is controlled by waves from said source,and means for producing imtplulses whose amplitude is controlled by saidrst named impulses.

7. The method which comprises producing a series of impulses of uniformamplitude and duration varied iii-accordance with a signal, causing eachof these impulses to produce another impulse of amplitude varied inaccordance with a signal, and utilizing the energy of the last mentionedimpulses to actuate a device for producing modulated waves of variableamplitude.

emma waves of high power which comprises first producing modulatedwaves. of low power, amplifying the power of said waves, converting thewave form during the power amplifying process, and restormg the waveform with greatly increased power at the close of the power amplifyingprocess.

10. The method of amplifying speech modulated waves .by means ofelectron discharge. devices and an inductance which comprises impressingthe waves upon successive electron discharge devices arranged in tandemand working each device at such potentials as tointroduce additional oddmultiple frequency components whereby squaretopped waves are produced,and impressing the resultant waves upon said inductance.

11. he method of signaling b means of two substantially uni-dlrectionaly conducting devices which comprises producing flattopped impulses inseries, controlling said impulses in accordance with signals, andemploying said impulses to commutate the flow of current from one. ofsaid devices to cause a flow of current'through the other .device.

12. In a system for signaling, means for forming two series offlat-topped impulses representing different portions of a modulatedwave, means for passing each of said series through arrangements forforming flat-topped waves, means I for producing waves from each of"said resultant series of flat-topped waves, and means forimpressingsaid waves upon a single transmission circuit.

13. In a system for signaling, means for forming two series offlat-topped impulses representing different portions of a modulatedwave, means for passing each of said series through an arrangement forforming flat-topped waves, means for producing waves from each of'saidresultant series of flat-topped; waves, and utilizing said waves tocontrol higher frequency waves.

, 14. "A modulating system comprising a discharge device, an inputcircuit for supplying thereto waves uniform in amplitude but variable inlength, and an output. circuit comprising elements whereby there arederived from said device waves variable in amplitude.

15. A system of modulation comprising means for producing'a carrierwave, means for converting said carrier wave into a flat top wave, meansfor modulating said fiat top wave in accordance with sound waves toproduce waves varying in length, means for converting said waves varyingin length into a wave varying in amplitude, means for suppressing saidcarrier wave, and means for impressing the modulated Wave on atransmission circuit.

16. A system of modulation comprising a high frequency generator forproducing a carrier wave, wave forming amplifiers for converting thecarrier waves into a flat top wave, means for modulating said fiat topwave in accordance with sound waves, to produce waves of constantamplitude but varying in length, means including inductance forconverting said fiat top waves varying in length into a wave of varyingamplitude, a filter for suppressing said carrier wave, and means forimpressing said modulated wave on a transmission circuit.

17 A system of modulation comprising a high frequency generator forroducing a carrier wave, means for converting said carrier wave into aflat top Wave, means for modulating said flat top wave in accordancewith sound waves to produce waves of constant amplitude but varyinglength, a circuit including an inductance, capacity and a unidirectionalconducting device for converting said fiat top waves of varying lengthinto a wave of varying amplitude, a filter for suppressing said carrierWave, and means for impressing said modulated wave on a transmissioncircuit.

18. A system of modulation comprising a high frequency generator forproducing a carrier wave, Wave forming amplifiers for convertingdifferent portions of said carrier wave into flat top waves, means formodulating said flat top waves in accordance with sound waves to produceimpulses of constant amplitude and varying length, means for convertingsaid impulses of varying length into waves of varying amplitude, andmeans for impressing said wave of varying amplitude upon a signaltransmission circuit.

19. A system of modulation comprising a high frequency generator forproducing a carrier wave, a plurality of setsof wave formers forconverting different portions of said carrier wave into flat top waves,means for modulating said fiat top Waves in accordance with sound wavesto produce waves of constant amplitude and varyinglength, a circuitincluding inductance, capacity and a unindirectional conducting devicefor converting saidflat top waves of varying len th into waves ofvarying amplitude, means or suppressing said carrier wave, and means forimpressing said modulated wave on a transmission circuit.

20. An amplifying system comprising an electron discharge device havingan output and an input circuit, a source of space discharge currentincluded in the output circuit, means in the input circuit for reducingthe current in the output circuit to zero in the absence of any appliedwaves in the input circuit, a circuit for impressing speech modulatedhigh frequency waves on said input circuit to be am lified by saiddevice and an outgoing circuit associated with the output circuit forconveying the amplified speech modulated high frequency waves.

In witness whereof, I hereunto subscribe my name this 1st da of August,A. D., 1923.

RAY 0ND A. HEISING.

